For realization of online nondestructive testing on cavity defects of logs

stress wave collected by acceleration sensor is analyzed by LabVIEW in the time domain. The speed and propagation time of stress wave can be acquired. 2D model is set up

use cell-based inversion method

improved Dijkstra algorithm and application of dynamic network planning in ray-tracing. The obtained 2D image. Algorithm based on interpolation is used to improve precision of inversion. And the median filtering algorithm is used to process the image. Experimental results show the method not only clearly reproduces internal cavity of the log but also has high precision.